给定动作，reducer 返回 undefined

Question

我正在开发我的第一个 react.js 应用程序。由于 Visual Studio 2017 中的 react 和 redux 模板项目存在一些问题，我最终在 Visual Studio 2017 中得到了一个 Web API 并且在 Visual Studio 中得到了一个完全不同的反应项目代码（我不知道这是否相关）。我正在尝试使用我的 Web API，但我的 action.payload.data 始终未定义。我也收到跨域错误。我不明白我做错了什么。

src/actions/index.js

import axios from 'axios';

export const FETCH_HOME = 'fetch_home';

const R00T_URL = 'http://localhost:52988/api';

export function fetchHome() {
    const request = axios.get(`${R00T_URL}/home`, { crossdomain: true });

    console.log(`request: ${request}`);
    return {
        type: FETCH_HOME,
        payload: request
    };
}

src/reducers/reducer_home.js

import { FETCH_HOME } from '../actions';

export default function(state = {}, action) {
    if (typeof action.payload === 'undefined') {
        console.log('action undefined');
        return state;
    }

    switch (action.type) {
        case FETCH_HOME:            
            console.log(`action: ${action}`);
            return action.payload.data;
        default:
            return state;
    }
}

src/components/home_index.js

import React, { Component } from 'react';
import { connect } from 'react-redux';
import { fetchHome } from '../actions';

class HomeIndex extends Component {
    constructor(props) {
        super(props);
    }

    componentDidMount() {
        this.props.fetchHome();
    }

    render() {
        console.log(`props: ${this.props}`);
        return (
            <div>
                <h1>Home Index</h1>                
            </div>
        );
    }
}

function mapStateToProps(state) {
    return { props: state.props };
}

export default connect(mapStateToProps, { fetchHome })(HomeIndex);

src/index.js

import React from 'react';
import ReactDOM from 'react-dom';
import { Provider } from 'react-redux';
import { createStore, applyMiddleware } from 'redux';
import { BrowserRouter, Route } from 'react-router-dom';
import reducers from './reducers';
import HomeIndex from './components/home_index';
import promise from 'redux-promise';

const createStoreWithMiddleware = applyMiddleware(promise)(createStore);

ReactDOM.render(
  <Provider store={createStoreWithMiddleware(reducers)}>
    <BrowserRouter>
      <div>
        <Route path="/" component={HomeIndex} />
      </div>
    </BrowserRouter>
  </Provider>
  , document.querySelector('.container'));

Answer 1

您对 axios.get() 的调用是异步的。

您可能希望动作创建者 return 动作对象，如下所示：

src/actions/index.js

...

export function fetchHome(result) {
  return {
    type: FETCH_HOME,
    payload: result
  }
}

...然后在您的组件中执行异步请求并使用结果调用操作创建者：

src/components/home_index.js

...

componentDidMount() {
  axios.get(`${R00T_URL}/home`, { crossdomain: true })
    .then(result => {
      console.log(`result: ${result}`);
      this.props.fetchHome(result)
    })
    .catch(err => {
      // Handle error
    })
}

...

如果你想在你的 action creator 中保留异步部分，那么看看使用 redux-thunk： https://www.npmjs.com/package/redux-thunk

给定动作，reducer 返回 undefined

Given action, reducer returned undefined

cross-domain

reactjs

axios